Recently, in fields such as wind turbine generator systems, it is required to ensure a power factor within a predetermined range, when electric power is supplied to a utility grid from a wind turbine generator system, in view of stabilizing the power supply in the utility grid.
Accordingly, for example, to keep a constant power factor, constant-power-factor regulation is performed for controlling the active power and the reactive power (for example, Japanese Unexamined Patent Application, Publication No. 2001-268805).    Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2001-268805